The present invention relates to apparatus and method for converting digital information into line segment displays on a cathode ray tube display. More particularly, the present invention provides electronic apparatus and method capable of converting digital information into visual line segments of normalized uniform visual intensity on a cathode ray tube display regardless of segment length and without variation of the CRT beam current.
While a variety of vector generators for converting digital information into line segments for visual display is known in the prior art, many generators utilizing cathode ray tube displays were characterized with drawbacks relating to the need to vary the beam current to maintain a visual display of uniform intensities for line segments of differing lengths. Those drawbacks stemmed from the fact that for a constant beam current the display intensity of a cathode ray tube is inversely proportional to the rate of beam deflection. For example, if both a long line segment and a short line segment required the same completion time, the drawing rate (the rate of beam deflection) for the short line segment would be slower than the rate for the longer line segment, and with a fixed beam current the short line segment would appear visibly brighter than the long line segment on the cathode ray tube display.
The various solutions to this problem were generally unsatisfactory because of complicated and expensive circuitry required to normalize visual intensity for line segments regardless of the length thereof. One widely known solution was to vary the intensity of the electron beam in accordance with the line segment length. The circuitry required to implement that solution was necessarily complex because of the wide range of beam currents required, typically greater than 1000 to 1. Also, correcting for visual intensity variations by varying the beam current alone is an inefficient solution because it still allows short line segments to take the same length of time for completion as a long line segment. Allowing the same length of time to draw a short line segment as a long one greatly reduces the number of short line segments that could have otherwise been drawn before refreshing the display.
Another solution calls for varying the drawing rate in accordance with line length. The circuits implementing that solution typically varied resistance or capacitance values, again a very difficult process. Some vector generators besides requiring different beam current and different resistance and capacitance values to draw different length line segments at uniform intensities and speeds, also require the beam current and component values to be varied while a line segment is in the process of being drawn, a still more difficult task.
Accordingly, an object of the present invention is to provide a cathode ray tube display of line segments in a digital format wherein the visual intensity is normalized for various line lengths without varying the intensity of the electron beam and without varying resistance or capacitance values.
Another object of the present invention is to draw line segments on a cathode ray tube display at a fast, efficient, normalized rate.
A further object of the present invention is to implement normalization of cathode ray tube visual display intensity of line segments of varying lengths with high speed digital circuitry.
A still further object of the present invention is to provide a digital vector generator which is uncomplicated, inexpensive to manufacture, and which has the stability and accuracy of a digital vector generator and the speed and line quality of an analog vector generator.